Viral hepatitis affects millions of people worldwide, and host immunity is the key determinant of patient outcome. Viral hepatitis can be life threatening in patients with haematological malignancy, including haemopoietic stem cell transplant recipients, because of the virus itself, or through a need to decrease the dose of chemotherapy. A past or currently infected haemopoietic stem cell donor could also transmit viral hepatitis. The burden of viral hepatitis in patients with haematological malignancies and the weak evidence on which previous guidelines are based has prompted the European Conference on Infection in Leukaemia (ECIL-5) to convene a group of experts in the fields of viral hepatitis and of haematological malignancy to specifically address previously unconsidered issues and grade the available quality of evidence according to the Infectious Diseases Society of America grading system. The group recommends that all patients should be screened for hepatotropic viruses before haematological treatment and that patients or haemopoietic stem cell donors with markers of past or current viral hepatitis should be assessed by an expert. Screening, vaccination, and treatment rules are reported in this Review.